The convertible rail-highway trailer to which the present invention relates has a body of conventional semi-trailer dimensions and is fitted with a coupling tongue at its front end and a female coupler at its rear end. In order to form a train of convertible trailers, a plurality of such trailers can be directly coupled end-to-end, in the manner disclosed in U.S. Pat. No. 4,202,454, or connected through an intermodal adaptor mounted on a conventional railtruck or bogie, as is disclosed in U.S. Pat. No. 4,669,391. The convertible trailer also includes a conventional king pin adjacent its front end for removable coupling to the fifth wheel of a tractor for the roadway mode of operation, thus forming an over-the-road tractor-semi-trailer combination.
As a consequence of dimensional requirements dictated by the need that such convertible trailers be both adaptable to their being pulled by a tractor when used in the roadway mode and by a locomotive or preceding railcar when in the railway mode, there is a difference in the centerline heights, relative to the top of the railroad track, between the tongue/socket connection and the locomotive railway coupling. Thus, it has been necessary to interpose a vehicle which makes the necessary height transition between the coupling components of a pushing or pulling locomotive and a first convertible trailer in a train of such trailers.
Heretofore, it has been known to create a transition vehicle by mounting a coupler socket at one end of a railway car and leaving the railway coupler at the other end of the car for pulling it by a locomotive. It is also known to adapt a convertible trailer by providing a normal railway coupler at the fore end thereof and a coupler socket at the rear end of the trailer. Each of these transition vehicles has attendant deficiencies. The use of a standard railway car results in a transition vehicle which is heavy, which must be moved on the track by a locomotive and which has performance characteristics incompatible with those of the convertible trailer it pulls. The use of a convertible trailer with a standard railway coupling at the fore end also presents an undesirable compromise. Although it provides the same performance characteristics as other intermodal vehicles in a train, it is large, expensive and incorporates elements, such as brakes for example, which may not be necessary to the limited role which the transition vehicle is called upon to perform.